Twogan

I have been looking at car batteries and smaller sealed lead acid batteries, however, I do come across a lot of ' car battery killed my arduino' posts. It seems using 12-14v input can make the on board regulator get too hot.

To remedy this I have been googling high capacity 9v batteries. I have come across many 'Electric fence Batteries'. like this :http://www.flytesofancy.co.uk/chickenhouses/Hotline_Saline_9v_Batteries.html

Instead of using the little heat generators, er, I mean linear voltage regulator, on the board, go with an off board switching regulator.They take in the higher voltage and efficiently convert it to 5V with very little battery power thrown away as heat.

See if you can locate this or something comparable at Farnell or your favorite source, and power your Arduino thru the 5V pin instead of thru the regulator.http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=811-2115-5-ND

The catch is that these batteries are not rechargeable so it makes for an expensive one-time use. Follow the previous recommendation and go for a switching regulator. That is by far the most efficient way to go.

Say your 5 volt load is a maximum of 200ma, then power requirement is 1 watt, which is 24watthours per day. So total requirement over 10 days is 240watthours. At 12 volts, that equates to around 20AH. Say you limit depth of discharge to 50%, to prevent irreversible battery damage, then you need a battery of at least 40AH.

Twogan

Of course. I see now the lack of recharge-ability ( rechargeableness ? is the downside.

I am making a one off installation that just needs to last 10 days. I assume that as they are single use I can run them all the way down and get nearly the whole capacity out of them without worrying about damaging the disposable battery.

This makes the pricing seem favourable again, and also being 9v I don't have to worry about overheating the arduino, and therefore dont have to get a stepping regulator.

I have managed to find out that an average electric fence uses about 60 milliamps of current, so do you think these Batts will manage outputting a continuous current between 90 and 200 milliamps ?

I don't think so. They are designed to provide power for several months which suggests lots of "small" current rather than a little of "large" current. Farmers do not like to be buying batteries every couple of weeks !!

What you are looking for is a relatively large current for a relatively short duration.

The battery chemistry may not be suited to such an application. You should contact the manufacturer to confirm their performance under your application.

For what it's worth, a car battery ( second hand if you must) and a £3 regulator is a far better option. If you must spend money buy a smallish solar cell to keep the battery "warm"

Another option is a 12v car battery and a series resistor. For example, if the maximum current draw is 200mA then you could use a 18 ohm 1 watt or 2 watt resistor to drop 3.6 volts, so the regulator gets a nominal 8.4 volts instead of 12. At 12v input and 200mA load the resistor dissipates 0.72 watts and the regulator dissipates 0.68 watts, instead of the regulator having to handle all 1.4 watts.

Yet another option is to put about 5 or 6 1N4001 or similar diodes in series with the battery. Each one will drop about 0.65v.

Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

marklar

I have battery power needs as well and have a 12v battery - here is my current direction.

Purchased some of these 12v to 5v power adapters with 1.2amp current capabilities. They should come in today or tomorrow.http://www.ebay.com/itm/250838285454?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_6598wt_1185

This is the battery:http://www.sears.com/shc/s/p_10153_12605_00911221000P?prdNo=1&blockNo=1&blockType=G1

The above battery ran a color cycle pattern on 70 LEDs for 45 minutes using an inverter. When the car chargers come in I will compare times and report the difference and any other issues / information that may be helpful.

Any ideas, suggestions or feedback on this power method is appreciated.

marklar

The above battery ran a color cycle pattern on 70 LEDs for 45 minutes using an inverter. When the car chargers come in I will compare times and report the difference and any other issues / information that may be helpful.

As per my last post - the car chargers work well. To save space I pulled off the end that goes into the cig socket and wired the black and red wires to the the 12v lithium icon battery mentioned in my last post. 4 of the chargers connected to the same 12v battery ran the suit for an hour. This is a 30% improvement over the inverter - with less space and no heat.

Not sure if this solution works for you, but reporting back as promised. Best of luck with your project.

Twogan

I am running an Arduino Uno with a Rogue Rmp3 shield attached and an Srf 04 sonic range-finder. The audio output from the Rmp3 is going into a little Kemo 12w audio amp, which is connected to a 8ohm/30 watt loudspeaker.

I need to power this lot for 10 days.

I have measured the Arduino/shield/sensor as needing 80mA 'at rest, and 110mA during playback ( the reading of the SD card is using this extra power I assume), this was tested with a 9v Battery plugged into the Arduino round power jack.

The audio amp is set at a low volume that is sufficient to playback speech at a reasonable level for listening at a 3m range. The amp/speaker are pulling 10mA 'at rest' and 80mA during playback. Surprisingly low, but the amp volume is way down.

I have worked this out over 10 days as requiring between 19.2AH and 26.4AH for the Arduino/shield/sensor, and between 2.4AH and 19.2AH for the amplifier.

I have purchased a Deep Cycle Leisure Battery which is 80AH capacity (so well over what I needed, but works out cheapest option compared to Sealed Lead Acid Deep Cycle Batts). I am also using a 12v solar charger.

I have heard that when fully charged these batteries can output over 14v, and possibly more with a solar panel attached, so to regulate the voltage I have run the power in to a L78S12CV 12v regulator. At this point I have taken a power line off to my Amplifier. However, before putting the power into the Arduino I have added a Pololu Step-Up/Step-Down Voltage Regulator S8V3A (as suggested by CrossRoads in another post I think..) to take the voltage down to an Arduino Friendly 8v.

http://www.pololu.com/catalog/product/2120

Hopefully this is a more efficient method of getting from 14+v down to 8v, than simply using a fixed (little heat generating) regulator....

Leisure Battery turning up tomorrow, so we will see if the theory works in practise.

I offer all this information in order to hear any views, alarm bells, tips.. etc and to possibly help any other beginners some info on car/leisure battery use..

Apologies for the length of the post, and any comments gratefully appreciated.